1. Field of the Invention
The present invention relates to minimizing electromagnetic interference (EMI) radiated from high-speed microprocessors operating at clock speeds at or exceeding 1 GHz.
2. Background Art
Europe requires electronic devices, such as microprocessor based systems, to comply with a European norm standard (EN-55022) that limits the amount of radiated EMI noise that can be radiated from the electronic device. The standard EN-55022 specifies different limits (on the order of dBxcexcV) based on the respective frequency bands. In particular, the standard EN-55022 specifies that devices operating at frequencies at about 1 GHz have a substantially stricter (i.e., lower) limit of radiated EMI noise than devices operating at frequencies substantially below 1 GHz. Hence, newer microprocessors operating at or above 1 GHz clock rates are more likely to fail the stricter radiated EMI limits specified by the standard EN-55022 due to the higher processor clock rates and harmonics radiated from the microprocessor buses.
A particular problem with EMI emissions in higher speed microprocessors involves the positioning of heat sinks overlying the microprocessor. The positioning of the heat sink directly above a microprocessor results in galvanic or capacitive coupling of the high frequency noise radiating from the microprocessor into the heat sink. Hence, the heat sink may effectively serve as an antenna for certain high frequency noise harmonics radiating from the microprocessor. In addition, the EMI emissions from the microprocessor may be capacitively coupled to cables in proximity to the microprocessor and the heat sink. Hence, EMI emissions may be radiated from the heat sink, and cables with the computer, especially from unshielded power cables. Consequently, if a computer fails the EN-55022 compliance tests, then it cannot obtain the CE approval necessary to market the computer in Europe.
There is a need for an arrangement that provides sufficient shielding of EMI emissions from higher speed microprocessor clocks to ensure compliance with prescribed EMI emissions standards.
There also is a need for an arrangement that shields EMI emissions from higher speed microprocessor clocks without modification of existing microprocessor socket designs, and that can be manufactured as a low-cost part using mass production.
There also is a need for an arrangement that shields EMI emissions from higher speed microprocessor clocks and provides a ground to minimize EMI emissions by the microprocessor heat sink.
These and other needs are attained by the present invention, where a microprocessor EMI shield is configured for isolating EMI emissions from the microprocessor, and grounding any electric potential caused by EMI emissions detected by the microprocessor heat sink. The microprocessor EMI shield includes a low-impedance conductive surface sufficient for conducting electric potential induced based on EMI emissions from the microprocessor. The microprocessor EMI shield also includes an array of apertures for accommodating the respective microprocessor pins, including microprocessor ground pins and microprocessor non-ground pins. The array of apertures includes a first group of apertures for accommodating the microprocessor non-ground pins, each having a spaced diameter for avoiding contact with the corresponding non-ground microprocessor pin, and a second group of apertures for accommodating the microprocessor ground pins. The second group of apertures each have a contact member configured for electrically connecting the corresponding ground pin to the low-impedance conductive surface, establishing a ground potential on the low-impedance conductive surface upon connection of the microprocessor pins with respective socket connectors. The low-impedance conductive surface also has an edge portion configured for engaging the microprocessor heat sink overlying the microprocessor, forming an enclosure for enclosing the microprocessor. Since the microprocessor heat sink also includes a conductive surface, the enclosure formed by the microprocessor heat sink and the microprocessor EMI shield provides a grounded shield to isolate EMI emissions from the microprocessor.
One aspect of the present invention provides a method of shielding a microprocessor. The method includes positioning a shield between a microprocessor, having microprocessor pins including ground pins and non-ground pins, and a microprocessor socket having socket connectors configured for receiving the respective microprocessor pins. The shield includes a low-impedance conductive surface sufficient for conducting electric potential induced based on EMI emissions from the microprocessor. The shield also includes an array of apertures including a first group of apertures configured for accommodating the respective non-ground pins and having a prescribed diameter for avoiding contact thereof, and a second group of apertures. The second group of apertures are configured for accommodating the respective ground pins and each having a contact member configured for electrically connecting the corresponding ground pin to the low-impedance conductive surface. The shield also includes an edge portion on the low-impedance conductive surface configured for engaging a microprocessor heat sink overlying the processor. The microprocessor pins are inserted through the array of apertures and into the microprocessor socket connectors, and the microprocessor heat sink is engaged with the edge portion to enclose the microprocessor. Hence, the microprocessor is enclosed between the shield and the microprocessor heat sink, enabling EMI emissions from the microprocessor to be isolated by the grounded shield and the ground microprocessor heat sink.
Another aspect of the present invention provides a shield configured for enclosing a microprocessor having microprocessor pins including ground pins and non-ground pins. The shield includes a low-impedance conductive surface sufficient for conducting electric potential induced based on EMI emissions from the microprocessor. The shield also includes an array of apertures including a first group of apertures configured for accommodating the respective non-ground pins and having a prescribed diameter for avoiding contact thereof, and a second group of apertures configured for accommodating the respective ground pins and each having a contact member configured for electrically connecting the corresponding ground pin to the low-impedance conductive surface. The shield also includes an edge portion on the low-impedance conductive surface configured for engaging a microprocessor heat sink overlying the processor. Hence EMI emissions from the microprocessor can be shielded by enclosing the microprocessor between the shield and the microprocessor heat sink, and inserting the microprocessor pins through the array of apertures into the microprocessor socket connectors, forming a grounded enclosure for the microprocessor.
Additional advantages and novel features of the invention will be set forth in part in the description which follows and in part will become apparent to those skilled in the art upon examination of the following or may be learned by practice of the invention. The advantages of the present invention may be realized and attained by means of instrumentalities and combinations particularly pointed in the appended claims.